As I can see it is not possible to delete file created with kha.Storage.namedFile(). I need this functionality and I think I can add it to some targets (flash, html5, Kore).
If the file does not exist kha.Storage.namedFile(filename).read() will return null.
But writing null kha.Storage.namedFile(filename).write(null) will just make no changes, so if the file existed it will remain the same with it's contents.
So for consistency it will be good to delete the file with kha.Storage.namedFile(filename).write(null).
Or I can just add function like kha.Storage.removeNamedFile(filename).